7) A
Quy đổi hh thành kim loại A (hóa trị n)
\(A\rightarrow A\left(NO_3\right)_n\rightarrow A_2O_n\)
\(n_{NO_3}=\dfrac{\left(m+62\right)-m}{62}=1\left(mol\right)\)
=> \(n_{A\left(NO_3\right)_n}=\dfrac{1}{n}\left(mol\right)\)
=> \(n_{A_2O_n}=\dfrac{1}{2n}\left(mol\right)\)
Ta có: \(n_A=n_{A\left(NO_3\right)_n}=\dfrac{1}{n}\left(mol\right)\) => \(M_A=\dfrac{m}{\dfrac{1}{n}}=m.n\left(g/mol\right)\)
Ta có: \(m_{A_2O_n}=\dfrac{1}{2n}\left(2.M_A+16n\right)=\dfrac{mn}{n}+8=m+8\left(g\right)\)
8) B
\(n_{H_2SO_4}=n_{SO_4}=\dfrac{86,6-29}{96}=0,6\left(mol\right)\)
\(\Rightarrow n_{H_2}=0,6\left(mol\right)\Rightarrow V=0,6.22,4=13,44\left(l\right)\)
9) D
\(n_{H_2SO_4}=0,1.0,5=0,05\left(mol\right)\Rightarrow n_{H_2O}=0,05\left(mol\right)\)
Theo ĐLBTKL: moxit + \(m_{H_2SO_4}=m_{muối}+m_{H_2O}\)
=> mmuối = 2,81 + 0,05.98 - 0,05.18 = 6,81 (g)
10) C
\(Ca+2HCl\rightarrow CaCl_2+H_2\)
\(MgO+2HCl\rightarrow MgCl_2+H_2O\)
Theo PTHH:
\(n_{HCl}=2.n_{Ca}+2.n_{MgO}=2\left(\dfrac{m_{Ca}}{40}+\dfrac{m_{MgO}}{40}\right)=2.\dfrac{20}{40}=1\left(mol\right)\)
=> \(V=\dfrac{1}{2}=0,5\left(l\right)=500\left(ml\right)\)
11) A
PTHH:
\(Mg+H_2SO_4\rightarrow MgSO_4+H_2\) (1)
\(Fe_2O_3+3H_2SO_4\rightarrow Fe_2\left(SO_4\right)_3+3H_2O\) (2)
\(MgSO_4+2NaOH\rightarrow Mg\left(OH\right)_2\downarrow+Na_2SO_4\) (3)
\(Fe_2\left(SO_4\right)_3+6NaOH\rightarrow2Fe\left(OH\right)_3\downarrow+3Na_2SO_4\) (4)
\(Mg\left(OH\right)_2\underrightarrow{t^o}MgO+H_2O\) (5)
\(2Fe\left(OH\right)_3\underrightarrow{t^o}Fe_2O_3+3H_2O\) (6)
Gọi số mol Mg, Fe2O3 là a, b (mol)
=> 24a + 160b = 20 (1)
Theo PTHH (1), (3), (5): \(n_{MgO}=a\left(mol\right)\)
Theo PTHH (2), (4), (6): \(n_{Fe_2O_3}=b\left(mol\right)\)
=> 40a + 160b = 28 (2)
(1)(2) => a = 0,5 (mol); b = 0,05 (mol)
Theo PTHH (1): \(n_{H_2}=0,5\left(mol\right)\)
=> V = 0,5.22,4 = 11,2 (l)
12) A
\(n_{Cu}=\dfrac{6,4}{64}=0,1\left(mol\right)\Rightarrow n_{SO_2}=0,1\left(mol\right)\Rightarrow n_{O_2}=0,05\left(mol\right)\)
=> \(V_{O_2}=0,05.22,4=1,12\left(l\right)\)
13) B
\(n_{H_2}=\dfrac{6,72}{22,4}=0,3\left(mol\right)\Rightarrow n_{H_2SO_4}=0,3\left(mol\right)\)
Theo ĐLBTKL: \(m_{KL}+m_{H_2SO_4}=m_{muối}+m_{H_2}\)
=> mmuối = 14,5 + 0,3.98 - 0,3.2 = 43,3 (g)
7)
Áp dụng ĐLBTNT: \(m_{-NO_3}=\left(m+62\right)-m=62\left(g\right)\)
\(\rightarrow n_{-NO_3}=\dfrac{62}{62}=1\left(mol\right)\\ \xrightarrow[]{BTNT.N}n_{NO_2}=1\left(mol\right)\)
PTHH:
\(4Fe\left(NO_3\right)_3\xrightarrow[t^o]{}2Fe_2O_3+12NO_2+3O_2\)
\(2Zn\left(NO_3\right)_2\xrightarrow[]{t^o}2ZnO+4NO_2+O_2\\ 2Cu\left(NO_3\right)_2\xrightarrow[]{t^o}2CuO+4NO_2+O_2\)
Theo PTHH: \(n_{O_2}=\dfrac{1}{4}n_{NO_2}=0,25\left(mol\right)\)
Áp dụng ĐLBTKL:
\(m_{oxit}=\left(m+62\right)-0,25.32-46=\left(m+8\right)\left(g\right)\)
=> Chọn A
8)
Áp dụng ĐLBTNT: \(n_{=SO_4}=86,6-29=57,6\left(g\right)\)
\(\rightarrow n_{=SO_4}=\dfrac{57,6}{96}=0,6\left(mol\right)\)
PTHH:
\(Mg+H_2SO_4\rightarrow MgSO_4+H_2\)
\(Zn+H_2SO_4\rightarrow ZnSO_4+H_2\)
\(Fe+H_2SO_4\rightarrow FeSO_4+H_2\)
Theo PTHH: \(n_{H_2}=n_{=SO_4}=0,6\left(mol\right)\)
=> V = 0,6.22,4 = 13,44 (l)
=> Chọn B
9)
\(n_{H_2SO_4}=0,5.0,1=0,05\left(mol\right)\\ \rightarrow n_{=SO_4}=0,05\left(mol\right)\)
PTHH:
\(Fe_2O_3+3H_2SO_4\rightarrow Fe_2\left(SO_4\right)_3+3H_2O\)
\(ZnO+H_2SO_4\rightarrow ZnSO_4+H_2O\)
\(MgO+H_2SO_4\rightarrow MgSO_4+H_2O\)
Theo PTHH: \(n_{O\left(oxit\right)}=n_{=SO_4}=0,05\left(mol\right)\)
Theo ĐLBTNT:
\(m_{muối}=m_{oxit}-m_O+m_{=SO_4}=2,81-0,05.16+0,05.96=6,81\left(g\right)\)
=> Chọn D
10)
Ta có: \(M_{Ca}=M_{MgO}\)
\(\rightarrow\overline{M_{hh}}=40\left(g\text{/}mol\right)\\ \rightarrow n_{hh}=\dfrac{20}{40}=0,5\left(mol\right)\)
PTHH:
\(Ca+2HCl\rightarrow CaCl_2+H_2\\ MgO+2HCl\rightarrow MgCl_2+H_2O\)
Theo PTHH: nHCl = 2nhh = 1 (mol)
=> \(V_{dd.HCl}=\dfrac{1}{2}=0,5\left(l\right)=500\left(ml\right)\)
=> Chọn C
11)
\(m_{hh.sau.các.pư}=m_{O\left(MgO\right)}=8\left(g\right)\\ \rightarrow n_O=\dfrac{8}{16}=0,5\left(mol\right)\\ \rightarrow n_{Mg}=n_O=0,5\left(mol\right)\)
PTHH: Mg + H2SO4 ---> MgSO4 + H2
0,5------------------------------->0,5
=> VH2 = 0,5.22,4 = 11,2 (l)
=> Chọn A
12)
\(n_{Cu}=\dfrac{6,4}{64}=0,1\left(mol\right)\)
Theo PTHH: \(n_{O_2}=\dfrac{1}{2}n_{SO_2}=\dfrac{1}{2}n_{Cu}=0,05\left(mol\right)\)
=> VO2 = 0,05.22,4 = 1,12 (l)
=> Chọn A
13)
PTHH:
\(Mg+H_2SO_4\rightarrow MgSO_4+H_2\)
\(Zn+H_2SO_4\rightarrow ZnSO_4+H_2\)
\(Fe+H_2SO_4\rightarrow FeSO_4+H_2\)
\(n_{H_2}=\dfrac{6,72}{22,4}=0,3\left(mol\right)\)
Theo PTHH: \(n_{H_2SO_4}=n_{H_2}=0,3\left(mol\right)\)
Áp dụng ĐLBTKL:
\(m_{muối}=14,5+0,3.98-0,3.2=43,3\left(g\right)\)
=> Chọn B
